LAGEOS, or Laser Geodynamics Satellites, are a series of scientific research satellites designed to provide an orbiting laser ranging benchmark for geodynamical studies of the Earth.
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The spacecraft are aluminium-covered brass spheres with a diameter of 60 cm and a mass of 411 kg, covered with retro-reflectors, giving them the appearance of giant golf balls. They have no onboard sensors or electronics, and are not altitude controlled. They orbit at an altitude of 5,900 kilometres (3,700 mi),[1] well above low earth orbit and well below Geostationary orbit.
Measurements are made by transmitting pulsed laser beams from Earth ground stations to the satellites. The laser beams then return to Earth after hitting the reflecting surfaces; the travel times are precisely measured, permitting ground stations in different parts of the Earth to measure their separations to better than one inch in thousands of miles.
The LAGEOS satellites make it possible to determine positions of points on the Earth with extremely high accuracy due to the stability of their orbits.
The high mass-to-area ratio and the precise, stable (altitude-independent) geometry of the LAGEOS spacecraft, together with their extremely regular orbits, make these satellites the most precise position references available.
The LAGEOS mission consists of the following key goals:
Ground tracking stations are located in many countries (including the US, Mexico, France, Germany, Poland, Australia, Egypt, China, Peru, Italy, and Japan) and data from these stations is available worldwide to investigators studying crustal dynamics.
There are two LAGEOS spacecraft, LAGEOS-1 launched in 1976, and LAGEOS-2 launched in 1992. As of 2004, both LAGEOS spacecraft are still in service.
The satellite (which will re-enter the atmosphere in 8.4 million years) also contains a plaque showing the arrangement of the Earth's continents in the past, present, and future.[2]
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